The present invention relates to a method of and a device for controlling an electric motor to actuate, through a transmitting mechanism, a movable member of a machine which has the movable member and an immovable member for supporting the movable member.
FIG. 1 is a block diagram of a first conventional electric motor control device.
According to the first conventional electric motor control device, servo operation command 15 as an input item is determined without recognizing mechanical vibration characteristics of a machine which has a movable member 7 and an immovable member 8, and motion command signal 9 is sent to servo device 3, which sends motion command signal 9 as operation command 12 to electric motor 5, which causes transmitting mechanism 6 to move movable member 7. If the electric motor control device cannot sufficiently perform the servo function, then servo operation command 15 is changed on a trial-and-error basis.
The first conventional electric motor control device needs a very long period of time to determine an optimum servo operation command.
FIG. 2 is a block diagram of a second conventional electric motor control device.
According to the second conventional electric motor control device, analyzing device 31xe2x80x2, input device 32, and output device 34 are added to the first conventional electric motor control device. Motion command signal 9 generated by analyzing device 31xe2x80x2, is sent as an analog signal to servo device 3, which sends motion command signal 9 as operation command 12 to electric motor 5, which causes transmitting mechanism 6 to move movable member 7. Rotation detector 4 sends rotation detector signal 10 through servo device 3 to analyzing device 31xe2x80x2. Analyzing device 31xe2x80x2 performs a fast Fourier transform on motion command signal 9 and rotation detector signal 10 to calculate frequency characteristics, determines analytical result 35, and determines servo operation command 15 based on analytical result 35.
According to the second conventional electric motor control device, as shown in FIG. 3, since motion command signal 9 generated by analyzing device 31xe2x80x2 has frequency components up to maximum frequency component frmax in excess of maximum measured frequency component fq, rotation detector signal 10 and analytical result 35 suffer an aliasing error representing components outside of the measured frequency range which are introduced when digital sampling is carried out. Therefore, the second conventional electric motor control device fails to determine accurate frequency characteristics.
Problems of the second conventional electric motor control device will be described in detail below.
As shown in FIG. 3, motion command signal 9 generated by analyzing device 31xe2x80x2 has frequency components up to maximum frequency component frmax which include those frequency components in excess of maximum measured frequency component fq. When motion command signal 9 having the frequencies shown in FIG. 3 is used, if mechanical resonances f4, f5 are present at frequencies higher than maximum measured frequency component fq and lower than maximum frequency component frmax, then motion command signal 9 excites mechanical resonances f4, f5 outside of the measured frequency range, and the components of mechanical resonances f4, f5 are contained in rotation detector signal 10. Because mechanical resonances f4, f5 have frequencies higher than maximum measured frequency fq, if digital sampling is carried out, then an aliasing error occurs to cause mechanical resonances f4, f5 to be observed apparently as f4xe2x80x2, f5xe2x80x2. Since analytical result 35 represents solid-line components with broken-line components added thereto, no proper frequency characteristics can be evaluated. When a signal having a frequency higher than maximum measured frequency fq is processed for digital sampling, an aliasing error occurs which causes a true high-frequency waveform to be recognized in error as a low-frequency waveform. The relationship between sampling interval xcex94t and maximum measured frequency fq is a known fact referred to as the sampling theorem, and is expressed by the equation (1) below. As a result, frequency characteristics including components that are not actually present are output as shown in FIG. 5.                               f          q                =                  1                      2            xc3x97            Δ            ⁢                          xe2x80x83                        ⁢            t                                              (        1        )            
For measuring the frequency characteristics of a conventional electric motor control device, it is necessary to have on hand an expensive instrument such as an FFT analyzer.
When an electric motor is operated, a movable member connected thereto is moved. The movable member of a load machine changes its characteristics depending on its position, causing a shift in the resonance frequency and the anti-resonance frequency which lower the accuracy with which to measure the frequency characteristics. In order to increase the amount of data to be measured for the purpose of averaging the data, it is necessary to collect data over a long period of time or carry out a plurality of operations and measurements. However, these requirements tend to cause problems in that the movable member moves increased distances and the measurement accuracy is further lowered, as shown in FIG. 7. Specifically, the position of the electric motor is greatly displaced from the start position due to the measurement, and hence the movable member is moved, changing the characteristics of the load machine. Consequently, the accuracy with which to measure the frequency characteristics is lowered, as when a peak is split as shown in FIG. 6.
FIG. 8 is a block diagram of a third conventional electric motor control device. The third conventional electric motor control device is different from the second conventional electric motor control device in that it has FFT analyzer 41 and signal generator 42 in place of analyzing device 31xe2x80x2, input device 32, and output device 34 of the second conventional electric motor control device.
The third conventional electric motor control device has FFT analyzer 41 and signal generator 42 in order to perform an electric motor control process in view of the characteristics of the machine. Motion command signal 43 generated by signal generator 42 is sent to servo device 3, which sends motion command signal 43 as control signal 12 to electric motor 5, which causes transmitting mechanism 6 to move movable member 7. Rotation detector 4 transmits rotation detector signal 10 via servo device 3 to FFT analyzer 41. FFT analyzer 41 receives motion command signal 43 from signal generator 42 and rotation detector signal 44 from FFT analyzer 41, and carries out a fast Fourier transform to calculate frequency characteristics. The operator reads an anti-resonance frequency and a resonance frequency from the calculated frequency characteristics, and determines servo operation command 15 based on the read frequencies. The operator needs to manually enter servo operation command 15 into servo device 3. Consequently, it has been customary for the operator to adjust the electric motor control device with a large expenditure of labor and time.
Heretofore, there have been various methods of tuning a mechanical control system having a flexible structure which is approximated by a two-inertia system. For example, Japanese laid-open patent publication No. 10-275003 discloses a vibration suppressing apparatus of a two-inertia resonance system for estimating a mechanical load speed and a disturbance torque through a obserber and suppressing vibrations based on the estimated mechanical load information in controlling a two-inertia system. The disclosed vibration suppressing apparatus has produced good results.
However, the conventional vibration suppressing apparatus has been problematic in that since parameters of the obserber and parameters of an PI (proportional plus integral) controller are adjusted individually, a lot of time may occasionally be required on a trial-and-error basis for adjustments.
It is an object of the present invention to provide an electronic motor control device which is capable of performing an electronic motor control process matching a controlled object without the need for an inspective analysis carried out by operators with professional knowledge and inspectors with professional knowledge in combination with a special instrument located outside of the electronic motor control device.
Another object of the present invention is to provide an electronic motor control device which calculates analytical results of proper frequency characteristics and performs an appropriate electronic motor control process easily and inexpensively.
Still another object of the present invention is to provide a method of controlling an electronic motor control device, which is capable of accurately measuring the frequency characteristics of a mechanical system.
Yet another object of the present invention is to provide an electronic motor control device which can suppress vibrations of a speed control system and which is capable of simultaneously adjusting parameters of a vibration suppressor and an I-P controller theoretically with one parameter easier than heretofore.
Yet still another object of the present invention is to provide an electronic motor control device which is capable of simultaneously adjusting parameters of a vibration inhibitor, a speed controller, and a position controller while achieving both an I-P control (integral plus proportional control) process and a PI control process for a speed control system and a position control system whose mechanical characteristics are of a two-inertia system.
A further object of the present invention is to provide an electronic motor control device which is capable of simultaneously adjusting parameters of a vibration inhibitor and a speed controller and a control parameter while achieving both an I-P control process and a PI control process for a speed control system for controlling a machine load speed and a position control system for controlling a machine load position, whose mechanical characteristics are approximated by a two-inertia system.
A still further object of the present invention is to provide a method of controlling an electronic motor control device, which is capable of adjusting the motor control device inexpensively and easily.
According to an aspect of the present invention, the frequency of any one of a motion signal equivalent to a motion signal sent from a servo device to an electric motor, a rotational speed signal of the electric motor, a position signal of a movable member of a machine, and a sensor signal representing the acceleration, speed, strain, etc. of the machine is analyzed, and a new electric motor control process is performed in view of the analytical result.
With the above arrangement, an electronic motor control process matching a controlled object can be performed without the need for operators and inspectors with professional knowledge.
According to a second aspect of the present invention, an analyzing device generates a motion command signal which does not contain unwanted high-frequency components outside of a measured frequency range so that no aliasing error is generated upon a frequency analysis, and analyzes the frequency of the motion command signal and the frequency of a rotation detector signal.
Since the motion command signal generated by the analyzing device contains frequency components lower than the maximum measured frequency, it does not excite mechanical resonances at frequencies higher than the maximum measured frequency. As the rotational detector signal does not contain frequency components higher than the maximum measured frequency and no aliasing error is generated, an anti-resonance point and a resonance point can properly be observed, and a correct analytical result is obtained. Therefore, the electric motor control device can be evaluated, making it possible to set a new servo operation command for carrying out an optimum electric motor control process.
According to a third aspect of the present invention, motion command signals output from a processing device to a servo device are executed symmetrically in normal and reverse directions of rotation of an electric motor.
With the above arrangement, a displacement of a movable member due to the operation of an electric motor is canceled out, thus removing causes of errors due to the position of the movable member at the time frequency characteristics are measured, so that the frequency characteristics can be measured accurately.
Of the motion command signals, low-frequency components have smaller amplitudes and high-frequency components have larger amplitudes, thus reducing the displacement of the movable member due to the operation of the electric motor, so that the frequency characteristics can be measured more accurately.
According to a fourth aspect of the present invention, a processing device calculates frequency characteristics from a motion command signal and a rotation detector signal, and a resonance frequency and an anti-resonance frequency are automatically calculated from the shape of the frequency characteristics. An electric motor control device is automatically adjusted based on the calculated results.
Only by using the processing device which is inexpensive and giving simple input information thereto, an appropriate electric motor control process is automatically adjusted easily and quickly.
According to a fifth aspect of the present invention, an electric motor control device has a speed controller for being supplied with a speed command, performing an I-P control process to determine a torque command in order to bring an electric motor speed into conformity with the speed command, a current controller for being supplied with a torque command and energizing an electric motor, and a detector for detecting an electric motor current and the electric motor speed, the electric motor control device also having a vibration suppressor for calculating a torsional angular speed from the electric motor speed and a machine load speed and suppressing vibrations using the torsional angular speed, and means for simultaneously adjusting parameters of the speed controller and parameters of the vibration suppressor.
With respect to a speed control system, one parameter value of speed loop gain Kv, integral time constant 1/Ti, torsional angle gain Ks, and torsional angular velocity gain Ksd is theoretically obtained. Therefore, the parameters of the vibration suppressor and the I-P controller can simultaneously be adjusted. The electric motor can be controlled in speed highly responsively while keeping a 2-inertia system stable without having to increase and lower a target response and exciting vibrations of a machine system.
According to a sixth aspect of the present invention, an electric motor control device has a speed controller for being supplied with a speed command and determining a torque command in order to bring an electric motor speed into conformity with the speed command, a current controller for being supplied with a torque command and energizing an electric motor, and a detector for detecting an electric motor current, an electric motor speed, and a machine load speed, the electric motor control device also having a vibration suppressor having a parameter xcex1(0xe2x89xa6xcex1xe2x89xa61) to continuously switch between an I-P control process and a PI control process, for calculating a torsional angular speed from the electric motor speed and the machine load speed and suppressing vibrations using the torsional angular speed, and means for simultaneously adjusting parameters of the speed controller and parameters of the vibration suppressor.
With respect to a speed control system and a position control system, the parameter values of speed loop gain Kv, integral time constant 1/Ti, torsional angle gain Ks, torsional angular velocity gain Ksd, and position loop gain Kp, which are effective for both the I-P control process and the PI control process, are easily obtained. Therefore, the parameters of the vibration suppressor, the speed controller, and a position controller can simultaneously be adjusted. If a target response is to be changed, then the parameters can be adjusted stably by changing a target response frequency xcfx89. A settling time can be shortened by changing "xgr" in association with parameter xcex1.
According to a seventh aspect of the present invention, an electric motor control device has a speed controller for being supplied with a speed command and determining a torque command in order to bring a machine load speed into conformity with the speed command, a current controller for being supplied with a torque command and energizing an electric motor, and a detector for detecting an electric motor current, an electric motor speed, and the machine load speed, the electric motor control device also having a vibration suppressor having a parameter xcex1(0xe2x89xa6xcex1xe2x89xa61) to continuously switch between an integral plus proportional control process and a proportional plus integral control process, for calculating a torsional angular velocity from the electric motor speed and the machine load speed and suppressing vibrations using the torsional angular speed, and means for simultaneously adjusting parameters of the speed controller and parameters of the vibration suppressor.
With respect to a speed control system for controlling a machine load speed and a position control system for controlling a machine load position, the parameter values of speed loop gain Kv, integral time constant 1/Ti, torsional angle gain Ks, torsional angular velocity gain Ksd, and position loop gain Kp, which are effective for both the I-P control process and the PI control process, are easily obtained. Therefore, the parameters of the vibration suppressor, the speed controller, and a position controller can simultaneously be adjusted. If a target response is to be changed, then the parameters can be adjusted stably by changing a target response frequency xcfx89. A settling time can be shortened by changing "xgr" in association with parameter xcex1.